Consolidating an older twin 115 HP FourStroke setup into a single Mercury 300 HP V8, either Verado (special-order) or Pro XS 4.6L, on a 23-foot cabin or walkaround boat typically runs $35,000–$42,000 all-in at Harris Boat Works in Gores Landing, less trade value on the two old motors. Timeline is 6–12 weeks depending on whether the customer picks Verado (special-order) or Pro XS (often quicker to source). Going single saves on service hours, fuel, and helm complexity for owners who don't need the redundancy of twins.
Last reviewed: 2026-05-24
Quick answer: Consolidating an older twin 115 HP FourStroke setup into a single Mercury 300 HP V8, either Verado (special-order) or Pro XS 4.6L, on a 23-foot cabin or walkaround boat typically runs $35,000–$42,000 all-in at Harris Boat Works in Gores Landing, less trade value on the two old motors. Build a quote at mercuryrepower.ca.
Consolidating an older twin 115 HP FourStroke setup into a single Mercury 300 HP V8, either Verado (special-order) or Pro XS 4.6L, on a 23-foot cabin or walkaround boat typically runs $35,000–$42,000 all-in at Harris Boat Works in Gores Landing, less trade value on the two old motors. Timeline is 6–12 weeks depending on whether the customer picks Verado (special-order) or Pro XS (often quicker to source). Going single saves on service hours, fuel, and helm complexity for owners who don't need the redundancy of twins.
Key facts
- Old setup: twin 115 HP FourStrokes, about 25 years old
- New setup: single Mercury 300 HP V8 Verado or Pro XS 4.6L
- Boat: 23-foot cabin / walkaround
- Cost range: $35,000–$42,000 CAD all-in (less trade)
- Timeline: 6–12 weeks
- Fuel economy: roughly 20–30% better at cruise vs two old 115s
- Deposit: $1,000 for big-block / Verado
- Warranty: Mercury Limited Warranty, confirmed at quote
What was on the boat before?
The candidate is a 23-foot cabin or walkaround (small cuddy, head, narrow side deck) that was rigged twin from new in the late 1990s or early 2000s. Twin 115 HP FourStrokes made sense at the time. Two motors, two of everything. Plenty of power for the hull, redundancy on big water, and a helm setup that felt premium for the era.
Twenty-plus years later the math has changed. The two 115s are running but showing their age, corrosion under the cowl, fading electronics, fuel pumps and water pumps being chased every season. The owner is paying two service bills, running two fuel lines, and replacing two of every consumable. The boat doesn't leave Rice Lake or the Trent system, so true offshore redundancy isn't actually being used.
Why consolidate twin 115s into a single 300?
The math comes out three ways.
Service cost, one motor instead of two cuts annual service hours roughly in half. One winterization, one spring service, one set of plugs and oil filters. Over a 10-year ownership window that's real money.
Fuel, a modern Mercury 300 V8 4.6L at cruise burns less fuel than two older 115s working at the same speed. Modern EFI tuning, better prop efficiency, and one motor instead of two reduces parasitic drag on the gearcase side. We typically see 20–30% better fuel economy at cruise on the conversion.
Helm simplicity, one throttle, one shift, one set of gauges. Docking a 23-foot cabin with twin throttles is a learned skill. Docking it with one V8 and Mercury's DTS at low speed is dramatically easier.
The trade-off is honest: no get-home redundancy. With one motor, if the motor fails offshore you wait for a tow. For Rice Lake, the Kawarthas, and the Trent system this is rarely a practical concern. For the open Great Lakes it's a real call to make.
What did the job involve?
A twin-to-single is one of the bigger jobs we do. We start with a transom inspection, twin bolt patterns leave eight holes that need to be addressed, sometimes filled and sometimes left for hardware reuse depending on where the single mounts. The center bridge between the twin pockets often needs reinforcement to handle the torque of a single V8 in the middle. This is shop work, not a one-day install.
The new motor goes through full Mercury rigging, DTS throttle, smart helm, hydraulic steering, new fuel routing from the tank to a single inlet, new gauge package. Propeller selection runs through 2–3 stainless props in the 15–16-inch diameter range, pitched 19–23 inches depending on hull and load, until WOT RPM lands in Mercury's band cleanly.
Water test on Rice Lake, loaded and unloaded, before pickup. Pickup-only at Gores Landing, we don't ship or deliver. The full timeline runs 6–12 weeks, the long end driven by Verado's special-order window.
What did it cost?
All-in lands between $35,000 and $42,000 CAD before trade. The motor itself sits in the $25,000–$28,000 band for Verado 300 or slightly lower for Pro XS 300 V8 4.6L. The DTS helm package, new steering, transom rework, controls, prop set, removal of two old motors, and water test build the rest.
Trade-in on two 25-year-old 115 FourStrokes depends heavily on condition, clean, running motors with reasonable hours can take meaningful dollars off. Fill the trade-in form and we email a CAD figure within one business day.
Financing is 7.99% APR over $10,000 on approved credit. A $1,000 deposit holds the order. See our cost guide for full repower pricing.
Frequently Asked Questions
- Why go from twin to single?
- Three reasons. Service cost, one motor to maintain instead of two. Fuel, a modern V8 300 burns less than two 25-year-old 115s pushed hard. Helm simplicity, one throttle, one shift, one set of gauges. The trade-off is no get-home redundancy, so it is the right choice for inland water and the wrong choice for far-offshore work.
- Do I need to modify the transom for single-engine conversion?
- Often yes. Twin transoms have two bolt patterns and a center bridge between them. We may need to fill the unused bolt holes, reinforce the center skin, and re-rig steering and controls for a single. This is included in the quote. We inspect the transom carefully before final quote.
- Can I trade in both old 115s?
- Yes. We take Mercury outboard trade-ins, and 25-year-old 115 FourStrokes still carry some core value depending on condition. Fill the trade-in form with details on both motors and we email a combined CAD figure within one business day.
- How long does a twin-to-single conversion take?
- 6–12 weeks depending on motor choice. If you pick Verado 300 the timeline is driven by Mercury's 8–14 week special-order window. Pro XS 300 V8 is often quicker. Transom rework adds about a week to either path. Pickup-only at Gores Landing.
Visit Harris Boat Works
Harris Boat Works · 5369 Harris Boat Works Rd, Gores Landing, ON K0K 2E0 · Phone (905) 342-2153 · Family-owned since 1947 · Mercury Platinum Dealer, selling Mercury since 1965.
We're the repower side of Harris Boat Works in Gores Landing, Mercury Platinum Dealer, selling Mercury since 1965. Twin-to-single is one of the most consequential repower decisions we walk customers through, and we walk through it honestly.
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